Air purifiers with built in particle sensors usually only have three to five fan speeds and a control system that is programmed to recognize only one sensor sensitivity setting. Depending on which country or region you are in, this sensor sensitivity setting may or may not be appropriate to keep your unit operating optimally.
For example, air in China can contain, on average, ten to twenty times more contaminants than air in the United States. An air purifier can be configured with a control system that is programmed to be less sensitive in this environment so that the air purifier will operate at its maximum level (i.e. the highest fan speed) when air is relatively dirty by China standards and will then operate at its minimum level (i.e. the lowest fan speed) when the air is relatively clean by China standards. However, if that same unit was operated in the United States where the air includes relatively less particulate, the control system would consider even the dirtiest air to be clean, and the unit would always either be off or operate at its lowest setting.
By contrast, if the control system in an air purifier is programmed to be more sensitive, the air purifier will operate at its maximum level (i.e. the highest fan speed) when air is relatively dirty by United States standards and then operate at its minimum level (i.e. the lowest fan speed or off) when the air is relatively clean by United States standards. However, if that same unit was operated in China where the air contains more particulate, the control system would consider even the cleanest air to be dirty, and the unit would always operate at its highest setting.
Some air purifiers are configured to visually indicate when the air is clean (for example by displaying a green light) or when the air is dirty (for example by displaying a red light). In addition, some air purifiers are configured to allow the control system to adjust the sensitivity of the sensor. Therefore, instead of having a sensor with only one sensitivity level which results in an absolute measurement for “clean air” and an absolute measurement for “dirty air,” there are a number of different sensitivity levels that may be adjusted by the user to cover the entire spectrum of air quality levels.
However, having multiple sensor sensitivities does not resolve the problem described above because, even if the user is allowed to adjust the sensitivity level of the sensor, the quality of the air fluctuates over time. Therefore, if a user adjusts the sensitivity of the sensor at one time and the air quality changes over the next day, hour or week, the user would need to continuously adjust the sensitivity as the quality of the air changed.
It is desirable, therefore to have an air purifier having a control system in communication with an air quality monitor, such as a particle counter, and also in communication with a sensor having a variety of sensor settings, wherein the control system adjusts the sensor setting so that the fan speed is continuously, automatically and appropriately adjusted as the quality of the air changes. This would provide a more efficient cleaning filter and allow users within different countries, or within different geographical locations within the same country, to utilize all available fan speeds and all available sensor settings of the purifier.